Flow Switch vs Pressure
Switch: Most of _'s spas use a
flow switch. If you have a 24/7 circulation pump
you likely have a flow switch. On a few models
the #1 Jet pump is 2 speed. On low it does the
heating. This design uses a pressure switch. In
both cases, the switches are simply on/off
switches. They tell the board if enough water is
moving pass the heater element. If not, the unit
will not turn the heater on and give a flow
error. What the board looks for is for the
switch to be OPEN when the pump is off. If so,
it turns the pump on and now looks at the switch
to be closed. If so, the board turns the heater
on. IF either situation is not true, the board
will not turn on the heater and will give an
error message.

Flow Switch: As
pictured, its a fairly simple to replace. It IS
directional. So make sure the arrows point in
the direction of water flow. On most the housing
is clear so you can see the switch. It consists
of 2 parts; the flap and the post. The post
remains stationary and contains the switch. The
flap is AWAY from the post when the pump is off
and against the post when the pump is on. A
clear housing allows you to see if that is true
and if not, gives indication to the problem.

Pressure Switch:
Most switches are adjustable. Problem is there
is a "sweet spot" that the switch must reside
in. If the adjustment is pass this sweet spot,
you will get errors.